Method of cutting patterns out of patterned fabrics with a cutting apparatus which includes a scanning device

ABSTRACT

Precise cutting of pattern strips and pattern pieces from lace and similar patterned fabrics requires correct mutual positioning of the fabric and fabric cutter for precise alignment with the boundary of the pattern pre-existing on the fabric. Patterned fabrics and especially loosely-woven lace are liable to randomly variable stretching and slippage which makes it impossible to cut under the direction of an externally imposed pattern program without regard to the instantaneous location of the pattern pre-existing on the fabric. The invention comprises lace-cutting apparatus and a lace-cutting method including optical scanning of the lace, recognition of the pattern boundary, and mutual alignment of the fabric with the fabric cutter to trace the intended cut line. Different techniques for mutual movement of the fabric and cutter are employed according to whether the pattern boundary is re-entrant or not. Preferred forms of fabric cutter include a hot-wire cutter and a laser beam cutter. The invention enables automatic high-speed cutting and trimming of lace and similar patterned fabrics.

This invention relates to apparatus and methods of cutting patternedfabrics, particularly but not exclusively patterned fabrics of the typeknown as lace.

The authoritative reference book "Textile Terms and Descriptions" by theTextile Institute of Manchester, U.K, defines "lace" on page 134 of itseighth edition (1986) as follows:

"lace:

A fine openwork fabric with a ground of mesh or net on which patternsmay be worked at the same time as the ground is formed or applied later,and which is made of yarn by looping, twisting, or knitting, either byhand with a needle or bobbin, or by machinery; also a similar fabricmade by crocheting, tatting, darning, embroidering, weaving, orknitting."

Whether formed by weaving, knitting or otherwise, lace and similarfabrics are commonly formed as a parallel-sided strip of a lengthusually very much greater than its width. The lace pattern may be formedas one or more pattern strips running along the length of the fabric,one or both sides of the pattern strip being scalloped or otherwisenon-straight along the edge of the pattern strip. Particularly where thelace pattern strip is in the form of a relatively narrow trim, aplurality of such lace pattern strips may be formed side-by-side acrossthe width of the as-woven (or as-knitted, etc) strip of fabric.Alternatively, the lace pattern may be formed on the fabric As a pieceor discrete area having a closed boundary (as distinct from a strip ofindefinite length). Again, a plurality of such discrete pattern piecesmay be formed across the width of the as-woven (or as-knitted, etc)strip of fabric, and a plurality of such discrete pattern pieces willcommonly be formed along the length of the fabric strip, however manypattern pieces may be formed across the width of the strip.

Pattern strips and pattern pieces may also be formed on the base fabricby techniques including but not restricted to selective dyeing,printing, embroidering, pile trimming or other localised modificationsof the base fabric and while not necessarily being "lace" as definedabove, such other patterned fabrics have in common with lace (for thepurposes of the present invention) the feature of pattern strips orpattern areas on the base fabric, each pattern strip or pattern areahaving a discrete boundary.

The common problem with lace and other such patterned fabrics is therequirement that each such pattern strip or pattern area (howeverformed) is required to be cut from the base fabric strip in a mannerwhich closely follows the pattern boundary, ideally without cutting intothe pattern strip or pattern area and without leaving attached portionsof the base fabric outside of the pattern strip or pattern area.

Therefore the problem requires an effective and efficient means ofcutting the base fabric strip along the boundary or boundaries of thepattern strips or pattern areas. It is an object of the presentinvention to provide apparatus and methods of cutting lace and similarpatterned fabrics which enable the cutting out of pattern strips andpattern areas along the boundary or boundaries of its pattern strips orpattern areas.

Hand cutting of lace strips and pieces is known, but requires thecontinuous and vigilant attention of a skilled person with considerablemanual dexterity, and is necessarily limited in the speed of cutting andthe rate of output of cut material.

Manually controlled cutting of embroidered fabric pieces with theassistance of a power-driven cutting tool is described in US4546546, butin this case, the path of the cut is under the sole control of theoperator and therefore has all the limitations of manual patternfollowing.

A machine for automatically cutting embroidered strips having thickenedscalloped edges is described in US3505917. However, this machine islimited to the cutting of strips and depends absolutely on the patternedstrips having thickened edges for control of the cutting path.Maloperation of this machine can be expected if the edges of the patternare not substantially thickened, and/or if other portions, which are notadjacent edges intended to be cut, are so thickened. Moveover, thismachine is not adapted to the cutting of pattern pieces havingboundaries which are closed and/or re-entrant.

GB1382541 describes a system for automatic laser cutting of garmentpieces from a strip of fabric, according to preselected, storedpatterns. While automating the cutting of predetermined patterns, thesystem of GB1382541 imposes externally determined patterns on the basefabric without regard to any pattern or surface features pre-existing onthe base fabric (see for example, FIG. 11a of GB1382541). This is incomplete contrast to the fundamental requirement of cutting out lacepatterns, where the path of the cut line is determined solely byfeatures pre-existing on the base fabric. Thus, the system of GB1382541is incapable of being applied to the cutting out of lace patterns, sincethe system of GB1382541 is incapable of determining where to cut byreference to a pattern preexisting on the base fabric.

US4972745 describes another automated system for cutting predeterminedpattern pieces from a strip of base fabric. In the system of US4972745,the strip of base fabric is advanced from a "machine Zero Point" on thebase fabric (FIG. 3). However, even if set up with data concerning theboundaries of lace patterns, and assuming a strip of uncut lace fabricto be initially aligned with the "Machine Zero Point", the system ofUS4972745 might start cutting the lace correctly, but would shortlydeviate from the correct cutting path because of the randomly variablestretching inherent in lace fabrics (which are loosely woven incomparison to garment textiles) and/or because of randomly variableslippage in the fabric-advancing mechanism (eg, driven fabric rollers).Thus with the system of US4972745, maintenance of a correct cut path inlace or similarly patterned fabric, and return to the correct cut pathafter deviation therefrom, is impossible owing to the lack of anyfacility in the system of US4972745 for tracing an actual intended cutpath pre-existing in the fabric to be cut (as distinct from a storednotional cut path, which cannot take, account of deviations in fabricposition from a nominal position).

In summary, while it might seem obvious to apply the automated patterncutting systems of the known prior art to the cutting out of lace andsimilar patterned fabrics, such known pattern cutting systems cannot beapplied to cutting patterns pre-existing on the fabric to be cut byreason of the complete absence of any means for tracing the pre-existingpattern. Mere storage and use of the notional pattern to be cut will notachieve a useful result, for the reasons given above.

According to a first aspect of the present invention there is providedapparatus for cutting lace and similar patterned fabrics having at leastone pre-existing pattern formed thereon, the or each said pre-existingpattern having a respective boundary defining an intended cut path, saidapparatus comprising fabric cutting means and relative positionvariation means for controllably varying the relative position of thefabric cutting means with respect to the lace or similar patternedfabric in two mutually orthogonal axes extending over the surface of thelace or similar patterned fabric, wherein said relative positionvariation means comprises bi-axially moveable mounting means for saidfabric cutting means, said apparatus further comprising a patternscanning means for scanning at least a selected area of said lace orsimilar patterned fabric, pattern recognition means coupled to saidpattern scanning means for recognising a pattern boundary pre-existingon said lace or similar patterned fabric within said selected area, andrelative position control means coupled between said pattern recognitionmeans and said relative position variation means for controlling therelative position of said fabric cutting means with respect to said laceor similar patterned fabric to cause said fabric cutting meanssubstantially to follow said intended cut path and to cut said lace orsimilar patterned fabric substantially along said intended cut path.

Said fabric cutting means may comprise a thermal cutting means which maybe constituted by a hot-wire fabric cutter or be constituted by a laserbeam fabric cutter.

Said relative position variation means preferably comprises means forcontrollably varying the position of said fabric cutting means acrossthe width of the strip of lace or similar patterned fabric, and forcontrollably varying the lengthwise positioning of said strip of lace orsimilar patterned fabric with respect to said fabric cutting means.

Alternatively, said relative position variation means may comprise meansfor controllably varying the position of said fabric cutting means bothacross the width and along the length of a strip or other piece of atleast temporarily stationarily positioned lace or similar patternedfabric, for example by use of a bi-axially movable mounting means forsaid fabric cutting means. In the latter case, said mounting means maybe capable of moving said fabric cutting means for a relatively shortdistance in the lengthwise direction of an extended strip of said laceor similar patterned fabric while said relative position variation meansis capable of moving said extended strip for a relatively long distancein the lengthwise direction thereof.

Said pattern scanning means preferably comprise an optical patternscanning means disposed to scan at least said selected area either in orwithout mechanical contact therewith. Said optical pattern scanningmeans may be mounted for conjoint movement with movement of said fabriccutting means relative to said lace or similar patterned fabric, andsaid selected area of the lace or similar patterned fabric includes thepoint operated upon by said fabric cutting means and is preferably smallin relation to said at least one pattern pre-existing therein.Alternatively, said optical pattern scanning means may be mounted in afixed position, and said selected area of the lace or similar patternedfabric includes the point operated upon by said fabric cutting means andis preferably large in relation to said at least one patternpre-existing thereon. As a further alternative, said optical scanningmeans may be mounted to scan a selected area which is ahead of the pointon said lace or similar patterned Fabric operated upon by said fabriccutting means in the direction of movement of said lace or similarpatterned fabric with respect to said fabric cutting means, and saidrelative position control means includes delay means to compensate forthe advance of said selected area with respect to said point in saidlace or similar patterned fabric operated upon by said fabric cuttingmeans.

Said apparatus preferably includes a fabric support and cutting surfaceover which said lace or similar patterned fabric is moved by fabricpropulsion means to pass beneath said fabric cutting means. Said fabricsupport and cutting surface may be either substantially planar orcurved, preferably being formed in the latter case as a cylinder whichmaybe rotatable. Said fabric support and cutting surface may beapertured in a region thereof aligned with said fabric cutting means toallow passage through the aperture of said fabric cutting operationthereof.

Said fabric propulsion means preferably comprises or is associated withfabric tension control means functioning to control tension in said laceor similar patterned fabric at least in the passage thereof across saidfabric support and cutting surface. Said fabric tension control meansmay comprise separate coarse speed controls for an uncut fabric pay-outroll and a cut fabric take-up roll, and a fine tension control in theform of a dancer roll or jockey roll acting upon said lace or similarpatterned fabric between said pay-out roll and said take-up roll. Saidfabric tension control means may additionally or alternatively comprisea localised fabric tensioner acting upon said lace or similar patternedfabric substantially only in the vicinity of the point thereof actedupon by said cutting means.

According to a second aspect of the present invention there is provideda method of re-entrant cutting of lace and similar patterned fabricshaving at least one pre-existing pattern formed thereon, the or eachsaid pre-existing pattern having a respective boundary defining anintended cut path, said method comprising the steps of controllablyvarying the relative position of fabric cutting means with respect tothe lace or similar patterned fabric in two mutually orthogonal axesextending over the surface of the lace or similar patterned fabric, saidmethod comprising the further steps of scanning at least a selected areaof said lace or similar patterned fabric to recognise a pattern boundarypre-existing on said lace or similar patterned fabric, and conjointlycontrolling the relative position of said fabric cutting means withrespect to said lace or similar patterned fabric to cause said fabriccutting means substantially to follow said intended cut path togetherwith controlling operation of said fabric cutting means to cut said laceor similar fabric: substantially along said intended cut path, saidmethod being characterised by reversing the direction or cutting whererequired to follow a re-entrant cut path.

Said selected area which is scanned may have its position variedconjointly with variations in position of said fabric cutting means, andsaid selected area is arranged to include the points on said lace orsimilar patterned fabric operated upon by said fabric cutting means andis preferably made small in relation to said at least one patternpre-existing thereon. Alternatively, said selected area may be scannedfrom a substantially invariant position and said selected area includesthe point on said lace or similar patterned fabric operated upon by saidfabric cutting means and is preferably made large in relation to said atleast one pattern pre-existing thereon. As a further alternative, saidselected area may be located for scanning ahead of the point on saidlace or similar patterned fabric which is operated upon by said fabriccutting means, in the direction of relative movement thereof withrespect of said lace or similar patterned fabric, and said conjointcontrol of relative position and of fabric cutting means operationdelayed to account for such advance.

Said lace or similar patterned fabric is preferably propelled across afabric support and cutting surface in a manner which controls thetension in said lace or similar patterned fabric. Said lace or similarpatterned fabric may be subjected to localised stretching thereof in aregion around the point thereon which is operated upon by said fabriccutting means, said region preferably being small relative to theoverall extent of said lace or similar patterned fabric.

Embodiments of the invention will now be described by way of example,with reference to the accompanying drawings wherein:

FIG. 1 is a plan view of the scalloped edge of a first lace strip;

FIG. 2 is a plan view of the scalloped edge of a second lace strip whichis a modified form of the first lace strip;

FIG. 3, 4 and 5 are respectively a plan view, a side elevation, and anend elevation of a first embodiment of lace cutting apparatus;

FIG. 6 is a plan view to an enlarged scale of part of the apparatus ofFIG. 3-5;

FIGS. 7 and 8 are respectively a fragmentary end elevation and afragmentary side elevation (both to a much enlarged scale) of parts ofthe apparatus of FIGS. 3-5;

FIGS. 9 and 10 are respectively a plan view and a side elevation of asecond embodiment of lace cutting apparatus;

FIGS. 11a and 12 are respectively a side elevation and an end elevationof a third embodiment of lace cutting apparatus; and

FIG. 11b is a fragmentary view, to a much-enlarged scale, of part of theapparatus shown in FIG. 11a.

Referring first to FIG. 1 this is a plan view of part of a first lacefabric strip 20 in the region of its scalloped edge 22 (shown as cutfrom an initially woven strip of uniform width, with the waste removed).The opposite edge of the strip 20 is not shown in FIG. 1, and theoverall length of the strip 20 is considerably greater than the partshown in FIG. 1. The principal feature to be observed in FIG. 1 is thatwhile the scalloped edge 22 deviates substantially and somewhatirregularly from a straight line in its as-cut form, the edge 22 is notre-entrant, ie, progressing along the edge 22 from one end of the strip20 towards the other end of the strip 20, at no point does the edge 22regress oppositely to the direction of this progression.

Referring next to FIG. 2, this is a plan view of part of a second lacefabric strip 30 in the region of its scalloped edge 32 (shown as cutfrom an initially woven strip of uniform width, with the waste removed).The strip 30 is basically similar to the strip 20 shown in FIG. 1, butdiffers in a certain fundamental respect concerning the nature of itsedge 32. As in FIG. 1, the scalloped edge 32 of FIG. 2 deviatessubstantially and somewhat irregularly from a straight line in itsas-cut form. However, in contrast to FIG. 1, the edge 32 of FIG. 2 isre-entrant, ie, progressing along the edge 32 from one end of the strip30 towards the other end of the strip 30, at certain points the edge 32regresses oppositely to the direction of this progression.

The practical significance of this fundamental difference (ie,non-re-entrant cut edges versus re-entrant cut edges) is that whenutilising a fabric cutter acting on the lace at a single point (in amanner analogous to a monobladed fratsaw), the edge 22 (FIG. 1) can becut by a combination of bidirectional cutter movement transverse to theedge with unidirectional longitudinal movement of the strip 20, whereasthe edge 32 (FIG. 2) can not be cut by such a combination ofbidirectional transverse cutter movement and unidirectional longitudinalfabric movement. This arises from the need to reverse the longitudinalmovement of the lace fabric strip 30 and/or to provide for an additionalcomponent of cutter movement in the longitudinal direction.

The first embodiment of lace cutting apparatus in accordance with thepresent invention (described below with reference to FIGS. 3-8) isessentially concerned with non-re-entrant edge cutting, of the basictype described above with reference to FIG. 1.

The second and third embodiments of lace cutting apparatus in accordancewith the present invention (described below with reference to FIG. 9-10and FIGS. 11a, 11b and 12 respectively) are enabled to providere-entrant edge cutting of the basic type described above with referenceto FIG. 2.

An extreme case of re-entrant edge cutting arises when the requirementis to cut out lace pieces having a closed boundary (eg, as shown in FIG.9), and the technical features of the second embodiment enabling it toperform lace piece cutting will also be described below.

Before proceeding to a detailed description of the various embodiments,it should be noted that while references will usually be made only tothe cutting of lace, such references should be understood as equallyapplying to the cutting of similar patterned fabrics, of the kindspreviously described, together with the cutting of other appropriatematerials having one or more patterns or other detectable markingspre-existing on them and defining one or more intended cut paths.

Having described certain fundamentals of the geometry of lace cuttingwith reference to FIGS. 1 and 2, reference will now be made to FIGS. 3-8for a description of the first embodiment 100 of lace cutting apparatus.

The apparatus 100 comprises a matt black plane-surface fabric supportand cutting platform 102 mounted on a tubular support framework 104. Atthe upstream end of the apparatus 100, (the left end as viewed in FIGS.3 and 4) laterally spaced brackets 106 extending horizontally outwardsfrom the support framework 104 rotatably carry a supply roll 108 onrespective pairs of spaced roll-shaft-mounting rollers 110.

Correspondingly, at the downstream end of the apparatus 100 (the rightend as viewed in FIG. 3 and 4) laterally spaced brackets 112 extendinghorizontally outwards from the support framework 104 rotatably carry atake-up roll 114 on respective pairs of roll-shaft-mounting rollers 116.

As shown in FIGS. 3 and 4, the supply roll 108 is wound with a lengthystrip 118 of as-woven lace which extends across the platform 102 to bere-wound on to the take-up roll 114. As woven, the lace strip 118 hasmutually parallel outer edges 120. The strip 118 is woven as twoside-by-side individual lace strips 122 and 124 each having a respectivescalloped edge 126 and 128 which are mutually interdigitated andinitially integral along a common boundary line 130 between their edges126 and 128.

The function of the apparatus 100 is to sever the individual lace strips122 and 124 one from the other, automatically and at high speed relativeto the cutting rates achievable by conventional manual cuttingtechniques.

To this end, a hot-wire cutter 132 is mounted on and forms part of theapparatus 100, the cutter 132 being arranged to intersect the lace strip118 on its passage from the supply roll 108 to the take-up roll 114.Propulsion of the lace strip 118 is undertaken by a drive roller 134disposed immediately beneath the strip 118 and controllably driven by avariable speed D.C motor 136. To hold the lace strip 118 against thedrive roller 134, a heavy free-running pinch roller 138 is mountedimmediately above the drive roller 134. The pinch roller 138 is freelyrotatably mounted on the outboard ends of a pair of pivot arms 140 whichrotate about a pair of pivot supports 142, one on each side of theapparatus 100. The two pivot arms 140 are mutually rotationally coupledby a torsionally stiff torque tube 144 such that the pivot arms 140 movethrough mutually equal angles to prevent the pinch roller 138 fromrocking as it rises and falls, ie, although the rotational axis of thepinch roller 138 has a variable height, this axis is kept horizontal atall times due to the prevention of differential height changes betweenone end and the other of the pinch roller 138.

At its end adjacent to the driver motor 136, the drive roller 134 ismounted in a spherical bearing block 146. A similar bearing block 148mounting the other (non-motor) end of the drive roller 134 can have itselevation controllably altered by operation of a motorised jacking unit150. Thus, unlike the pinch roller 138, the rotation axis of the driveroller 134 can be controllably rocked by a small amount about thelongitudinal axis of the apparatus 100 (aligned left/right as viewed inFIGS. 3 and 4). Such controlled rocking of the drive roller 134 enablescontrolled variation of the transverse location of the pinch point ofthe roller pair 134/138 on the fabric strip 128 passing therebetween,and hence a controllable variable lateral skewing of the fabric strip118 enabling steering thereof as it is propelled through the apparatus100.

A pair of sensors 152 (FIG. 3) mounted on a transverse gantry 154 overthe platform 102 continuously monitor the lateral positions of thefabric strip edges 120, and cause appropriate operation of the jackingunit 150 to keep the strip 118 substantially centralised as it ispropelled through the apparatus 100.

As is most clearly shown in FIG. 5, the hot-wire cutter 132 is suspendedat the upper end 156 from the gantry 154, and is anchored at its lowerend 158 to the lower reaches of the support framework 104. The cutter132 comprises a relatively short unclad resistance wire 160 which passesthrough a transverse slot (not shown) formed in the platform 102. Thelower end 162 of the resistant wire 160 is tethered by an electricallyinsulating cord 164 to the lower end 158 of the cutter 132 where it islaterally anchored by transverse guy cords 166 to the support framework104.

The upper end 156 of the cutter 132 (coincident with the upper end ofthe resistance wire 160) is secured to a transversely aligned drivecable 168 which is formed as a continuous loop tautly suspended betweena drive pulley 170 and an idler pulley 172. The drive pulley 170 iscontrollably rotated by a stepper motor 174 or other suitable servomotor. The pullies 170 and 172, together with the motor 174 are suitablymounted on the gantry 154.

Notwithstanding that the lower end 158 of the cutter 132 issubstantially immobile, the ability of the upper end 156 to becontrollably traversed by appropriate operation of the motor 174 enablesthe transverse portion of the resistance wire 160 in relation to theremainder of the apparatus 100 to be controlled.

Flexible flying leads 176 and 178 electrically connected respectively tothe upper and lower ends 156 and 162 of the resistance wire 160 enablethe wire 160 to be electrically heated by the passage therethrough of anelectric current of appropriate magnitude and thereby undertake thermalcutting of a selected point on the lace strip 118. (Details concerningmaterials incorporated with lace strip 118 and of selection of currentlevels to facilitate thermal cutting of lace will be discussedsubsequently).

Selected details of the hot-wire cutter 132 are shown to enlarged scalesin FIGS. 6, 7 and 8 which are respectively a front elevation of theupper end of the cutter 132 (including the drive cable loop 168 and itsmounting pullies 170, 172), a fragmentary front elevation of the upperand lower ends 156 and 158 of the cutter 132 (together with parts ofadjacent cords, cables, and tethers), and a fragmentary side elevationof the resistance wire 160 (and of its adjacent connections).

In order to provide appropriate information for the correct automaticcontrol of the transverse position of the resistance wire 160, anoptical scanner 180 is located on top of the lace strip 118 to overliethe scalloped edges 126 and 128. The horizontal location of the scanner180 in both transverse and longitudinal directions is substantiallyfixed by a pair of trailing arms 182 attached at their downstream endsto the scanner 180. The upstream ends of the trailing arms 182 aremounted in respective horizontal pivots 184 to allow vertical movementof the scanner 180. A torsion control system 186 enables theweight-induced pressure of the scanner 180 on the lace strip 118 to bestatically and dynamically optimised to allow the scanner 180 to "float"on the lace strip 118 without significantly dragging on the strip 118.Since the threads of which lace is formed are customarily white oranother relatively light colour, and moreover the lace is of relativelyopen structure (at least in the boundary areas between adjacentindividual strips of lace), then the optical scanner 180 can readilydetect the lace of the strip 118 against the matt black surface of thefabric support and cutting platform 102. In particular, the scallopededges 126 and 128 can readily be optically detected by the scanner 180.Readout from the scanner 180 is processed in an associated signalprocessing and control circuit 188 (FIG. 4) forming part of theapparatus 100. (Note that the connections between the scanner 180 andthe control circuit 188, and other such power, signal, and controlconnections are omitted from the drawings for the sake of clarity).

The signal processing and control circuit 188 is programmed or otherwiseset up to detect the instantaneous position of the common boundary line130 of the individual lace strips 122 and 124 between their respectivescalloped edges 126 and 128, with respect to the scanner 180 and henceto the apparatus 100 as a whole. The circuit 188 is also set up to takeaccount of the upstream separation of the scanner 180 from the cutter132, and further to take account of the speed of the lace strip 118across the platform 102. The position information representing thedetected position of the common boundary line 130 is delayed by a periodproportional to the separation/speed ratio, and fed to the motor 174 todrive the hot wire 160 to an appropriate transverse position which willcut the as-woven lace strip 118 into mutually separate individual lacestrips 122 and 124 by severing the strip 118 along the pattern line 130.The mutually separated individual lace strips 122 and 124 are conjointlywound on to the take-up roll 114.

An appropriate magnitude of electric current to be fed through theresistance wire 160 (via the flexible flying leads 176 and 178) tooptimise the temperature of the wire 160 can be determinedexperimentally and controllably varied to suit instantaneous parametersof fabric speed, fabric weight, and actual fabric cutting speed (neverless than the linear speed of its lace strip 118 through the apparatus100 and greater by a factor dependent on the complexity of the patternboundary line, particularly its true length). To the extent that anincrease in fabric cutting speed over fabric strip speed is demanded dueto output from the scanner 180, the short time lag before the actualresultant: cut is made can compensate for the thermal lag of theresistance wire 160 as it is more strongly heated by an electric currentincreased to take account of demanded extra cutting effort. (Note thatit is desirable to maintain the wire 160 at an appropriate temperaturesince if the wire 160 is too hot, the lace will be discoloured, and ifthe wire 160 not hot enough, it will produce a hard melted/resolidifiedcut edge with a tendency to fibre pulling with resultant puckering).

The linear speed of the lace strip 118 through the apparatus 100 iscontrolled by the roller drive motor 136, and set up according to thetype of fabric to be cut and the complexity of the pattern line to befollowed. Where the individual lace strips have deeply scalloped edges,a lower fabric advance speed will be preferable to allow for theincreased transverse deviations of the fabric cutter.

Referring now to FIGS. 9 and 10, these respectively illustrate a planview and a side elevation of the second embodiment 200 of lace cuttingapparatus in accordance with the invention. By contrast to the firstembodiment 100 (wherein a hot-wire cutter capable only ofone-dimensional transverse movement was employed to cut a non-re-entrantline between two side-by-side individual lace strips), the secondembodiment 200 utilises a laser beam fabric cutter to cut out lacepieces 202 (FIG. 9) each having a closed boundary. However, in thesecond embodiment 200 the general structure of the fabric supportplatform, the pay-out and take-up rolls, and the fabric/propulsionrollers are the same as in the first embodiment 100 and theirdescription will therefore not be repeated.

A basic difference in operation of the second embodiment 200 compared tooperation of the first embodiment 100 arises from the necessity of thefabric cutter to trace a closed boundary path, and hence the fabricstrip is not continuously transported through the apparatus; instead thefabric is moved in steps, being held stationary during cuttingoperations and moved only between cutting operations. The fabric cutteris mounted for controlled movement over the fabric in a two-dimensionalcombination of transverse and longitudinal movements, of an extentsufficient to cover the full width of the un-cut strip and to cover atleast one pattern extent in the longitudinal direction.

Accordingly, the apparatus 200 has a cutting head 204 mounted for suchcombined bi-axial movement on a bi-directionally movable gantry 206generally similar to the plotting mechanism of an x-y graphical plotter.

Longitudinal movement of the cutting head 204 is controlled by a steppermotor 208 which drives the gantry 206 by means of a drive cable 210.Transverse movement of the cutting head 204 is controlled by a stepperMotor 212 which drives the cutting head by means of a drive cable 214.This drive arrangement requires that for every unit of longitudinaldisplacement, one unit must be subtracted from the transversedisplacement (as is normal in x-y plotters).

The cutting head 204 is a combined mirror and focussing lens systemwhich receives, deflects and focuses a laser beam 216 onto theappropriate point of the fabric being cut. The laser beam 216 originatesin a low-power continuous-output carbon dioxide laser 218 (FIG. 10)vertically mounted on the apparatus 200. The upwardly-directed outputbeam 216 from the laser 218 is deflected into a horizontal longitudinaldirection by a fixed mirror 220 (FIGS. 9 and 10), deflected into ahorizontal transverse direction by a further mirror 222 carried on thegantry 206, and finally through the mirror/lens cutting head 204 ontothe fabric.

An overhead television camera 224 (FIG. 10) is mounted above the cuttingregion to include in its downwardly directed field of view at least thearea which can be moved over by the cutting head 204 in its range ofmovements. The camera 224 (which is preferably a CCD camera) suppliesoptical scanning signals to a signal processing and control unit 226forming part of the apparatus 200.

The unit 226 is preprogrammed to recognise the outline of the lacepattern pieces 202 and to correct the position of the cutting head 204in accordance with camera-detected displacements and stretch-induceddistortions of the pattern pieces 202 so as to closely trace theirboundaries during cutting operations. The unit 226 also controls thelevel of the output power of the laser 218.

Not shown in FIGS. 9 and 10 are items such as a fume extraction systemand safety interlocks to ensure that the laser beam 216 has a clearworking path.

Before proceeding to a detailed description of the third embodiment oflace cutting machine in accordance with the present invention (FIGS.11a, 11b and 12), some discussion of its underlying designconsiderations and operating principles will be given below.

The machine of the third embodiment has been configured to be of compactdimensions, and to be capable of profiling a range of lace patterns andtypes. The cutting medium illustrated is a low power C02 laser but couldincorporate, for example, a hot-wire fabric cutter.

For the majority of lace patterns the fabric is assumed to pass underthe cutting head such that the head can follow the required cutting pathby simple lateral motions i.e. non-re-entrant as FIG. 1.

It is known however that there are patterns in which the cutting pathturns backwards relative to the direction i.e. re-entrant as shown inFIG. 2. This would require the direction of fabric movement to betemporarily reversed, or the laser cutting head to be driven briefly inthe direction of material travel.

It is believed that reversing such a lightly woven material as lacewould cause it to stretch and hence a modified version of thenon-reversing fabric propulsion of the first embodiment has been devisedfor the third embodiment.

In the third embodiment an optical or other suitable sensor array isused to recognise the position of the path on the fabric to be cut ortrimmed, relative to previously supplied information on the lace patternbeing processed.

Clearly, detection and cutting cannot be coincident and hence thecutting station must be a distance downstream. The cutting path controlsignal is electronically delayed to allow for this offset and thus it isimportant that the distance be accurately controlled.

It is believed that two factors will be important here: firstly that thefabric tension be controlled, and secondly that the offset distance beminimised, such that any variations in fabric tension will have minimalstretching effect to minimise effective variations in the offsetdistance.

In the third embodiment the fabric being cut is led over a highlypolished cylindrical support surface in which a lateral slot has beencut to provide an exit for the laser cutting beam. The pattern detectionarray is an optical device of the reflective or broken beamemitter/detector type. The broken beam arrangement will use a window oraperture while the polished support surface will provide the requiredreflection.

Tension control is primarily by speed control drives to both the inputand output bales, by providing micro-textured fabric guides, and by finetuning the fabric tension through a conventional dancer roller-basedcontrol system adjusting the take-up bale speed.

For re-entrant patterns, the laser cutting head is rocked about thecentre of the cylindrical support surface, moving as one with thecylinder, the sensor head, the cutting slot and the cutting headcarriage and rails. The combination of the lightly textured guidesrelative to the polished support surface will minimise the stretchingeffect during the rocking action.

Referring now to FIGS. 11a, 11b and 12 the illustrated machine 300 issized to handle fabric bales having a width of approximately 1 metre.The same general principles would apply to a machine dedicated tonarrower material.

The machine frame 301 is a self-contained structure providing all thesupport and attachment points for the machine components.

The input bale 302 is mounted in a rolling vee-block arrangement 303 inwhich three of the rollers 304 are free-running and one of the rollers304 is motor-driven by a motor 305. The input bale spindle is furnishedwith grooves 306 which locate on the rollers 304 to provide laterallocation of the spindle.

The rolling vee-blocks 303 are mounted on a parallelogram arrangement307 which is positioned laterally by a motor and jack screw arrangement308.

This mechanism 307 forms part of a fabric centring system taking itscontrol signals from fabric edge sensors 309.

The fabric unrolling from the input bale 302 passes up over a glide 310,which may be manufactured from fine grade brushed and hard-anodisedaluminium alloy. The guide 310 may be rotated at a very low speed tospread the position of the wearing surface.

The fabric then passes onto a cylindrical support surface 311 which is ahighly finished and spectrally polished component. The cylinder 311 ismounted on free-rolling supports 312 at both ends, with its angularposition being driven and controlled by a stepper motor 313 and a wirecable system 314.

For some particularly finely woven fabrics a local tensioner 330 isfitted in the cutting slot in the cylinder 311. This has the effect oflocally stretching and magnifying the area being cut.

The laser 315 in this third embodiment is mounted co-axially with thecylinder 311 and may be attached to the machine frame, along with itsdiverging optics 316 and associated electronics and accessories.

The output beam from the laser 315 is folded through a pair of facereflecting mirrors 317 and 318 which are mechanically attached to thecylinder 311.

The laser beam then travels to a traversing lens carriage 319 whichcomprises a mirror 320 and focussing optics 321 to converge the beamdown onto the cutting point on the fabric.

The traversing lens carriage 319 is guided on rails 329 which aremechanically attached at their ends to the cylinder 311 and positionedsuch that the cutting point is at all times over the cutting slot in thecylinder 311.

The carriage 319 is driven laterally by a stepper motor 322 and cablesystem under instructions from the pattern recognition electronics. Asensor array 323 is mounted immediately upstream of the cutting point,and positioned laterally to cover the width of the pattern beingprocessed. The sensor array 323 may be attached to the machine frame, ormoved with the oscillations of the cylinder 311.

As the cut fabric comes off the cylindrical support surface 311, ittravels over a guide 324 which is exactly as described for the guide310.

A tension jockey or dancer roll 325 is positioned between the cylinder311 and the guide 324. This accurately measures the material tension andprovides information to input and output bale drive motors 331 and 332to maintain precise tension control.

The cut fabric is collected on a takeup bale 326 which is mounted on amotor-driven and rolling vee-block system similar to the input balearrangement.

The speed of fabric movement is monitored by tachometer rollers 327 and328 which bear directly on the input and output bales 302 and 326. Inthis way they measure the fabric speed irrespective of the balediameters.

Operation of the lace cutting machine 300 is as follows:

When a particular pattern of lace is loaded onto the machine 300,information in the form e.g. of a floppy disc is read into the machinecontrol processor.

The sensor array 323 is adjusted to centre on the pattern to be cut. Asfabric is run under the sensor array 323, the system recognises theborder to be cut or trimmed, and with information on the fabric speed,produces the required offset and movement instructions to the cuttinglaser head assembly 320/321.

For non-re-entrant patterns the support surface 311 remains static, butfor re-entrant patterns (and creative work), the system recognises thatthe cutting path has curved back and hence activates the rocking actionas required.

Compared to the first and second embodiments 100 and 200, the machine300 has been altered to be of more compact dimensions but to retain thesimplicity and economy of construction of the basic design.

The control of fabric tension is improved by the system of driving boththe input and the output bales plus the addition of micro-textured guiderollers which give friction control to the lace as it passes over them.

The fabric guidance is further improved by a centering system whichtakes a signal from edge sensors and moves the input bale axially on itsvee-block mount as it is feeding lace onto the cutting area.

The large flat cutting table has been replaced by a cylindrical supportsurface which adds to the tension control now in the area local to thecutting beam.

Fabric control is further enhanced by means of a dancer roller which canadjust the bale speeds by signalling variations in the tension of thelace after the cutting operation.

Pattern recognition has been improved by use of a sensor arraypositioned immediately upstream of the cutting area and just above thelace surface which it recognises as it moves over the cylinder.

The cutting of patterns which turn backwards relative to the directionof movement of the fabric (ie. which are re-entrant) is now achieved byrocking the whole cutting head assembly as instructed by the patternsensors, thus presenting the cutter with the re-entrant route. This hasthe benefit of fixing the relative positions of the cutting head, thesensor, and the cutting slit (the cutting position). The effect ofstretching of the lace is minimised by the nature of the polishedsurface of the cylinder.

The X-Y movement is replaced longitudinally by the aforementioned systemand the lateral or Y movement by a carriage on rails which positions thecutting beam over the slot in response to signals from the sensor array.

The handling of finely woven and narrow strip fabrics is enhanced by atensioning insert 330 (FIG. 11b) which is fitted into the cutting slotto provide additional localised tensioning of the lace by slightstretching.

Compared to the prior art manual cutting systems, the lace cuttingapparatus and methods of the present invention have the prime advantageof increased cutting speed; 20 metres/minute versus 4-5 metres/minutefor previous systems.

There are also the merits of simplicity and economy of construction.

The advantage of the route recognition system allows for a greater andever-increasing range of work. Patterns can be stored in memory for usein the future. The occurrences of fabric stretch and mis-positioning canbe corrected electronically in the more complex laser cutter with thelaser optics being directed around the actual required cutting path.

While certain variations and modifications have been described above,the invention is not restricted thereto, and other modifications andvariations can be adopted without departing from the scope of theinvention as defined in the appended claims.

We claim:
 1. A method of re-entrant cutting of patterned fabrics havingat least one pre-existing pattern formed thereon, each said pre-existingpattern having a respective pattern boundary defining an intended cutpath, wherein said intended cut path at least closely approximates saidpattern boundary, said method comprising the steps of:providing acutting apparatus, said cutting apparatus including a support surface, afabric cutting means operatively mounted for movement above said supportsurface, and a scanning means mounted above said support surface,positioning said patterned fabric on said support surface, saidpatterned fabric having a longitudinal axis and a transverse axis,scanning at least a selected area of said patterned fabric with saidscanning means to identify a location of said pattern boundarypre-existing on said patterned fabric, and cutting said patterned fabricwith said fabric cutting means by:positioning said fabric cutting meanswith respect to said pattern boundary so that said fabric cutting meansintersects said patterned fabric substantially on said intended cutpath, and moving said fabric cutting means with respect to saidpatterned fabric to cause said fabric cutting means to cut saidpatterned fabric while following said intended cut path along saidpattern boundary, wherein said moving step includesmoving said fabriccutting means in a combination of directions which includes bothdirections of the transverse axis and both directions of thelongitudinal axis of the patterned fabric, and maintaining said fabriccutting means substantially on said intended cut path by continuouslytracking with said scanning means the location of said pattern boundary,and continuously correcting the position of the fabric cutting means asrequired to maintain the position of said fabric cutting meanssubstantially on said intended cut path.
 2. A method of re-entrantcutting as set forth in claim 1, wherein a portion of said patternedfabric is positioned in a working area on said support surface, and saidscanning and cutting steps are performed in said working area, themethod further comprising,moving said patterned fabric after cutting ofsaid portion of patterned fabric in said working area to bring anotherportion of the patterned fabric into said working area.